1. Technical Field of the Invention
The present invention relates to novel diorganosiloxane compounds containing a 4,4-diarylbutadiene functional group.
The present invention also relates to the formulation of these diorganosiloxane compounds containing a 4,4-diarylbutadiene function into cosmetic compositions useful for screening out UV-A radiation.
This invention also relates to photoprotective compositions comprising diorganosiloxane compounds containing a 4,4-diarylbutadiene function, as sunscreens that are active in the field of UV radiation and more particularly in the field of UV-A rays.
2. Description of Background and/or Related and/or Prior Art
It is known that radiation with wavelengths of from 280 nm to 400 nm permits tanning of the human epidermis and that radiation with wavelengths of from 280 to 320 nm, which is known as UV-B radiation, causes skin burns and erythema that may be harmful to the development of a natural tan. For these reasons and also for aesthetic reasons, there is increasing demand for means for controlling this natural tanning. This UV-B radiation should thus be screened out.
It is also known that UV-A rays, with wavelengths of between 320 and 400 nm, which cause browning of the skin, are liable to induce impairment in the skin, especially in the case of sensitive skin and/or skin that is continually exposed to sunlight. UV-A rays in particular result in a loss of elasticity of the skin and the appearance of wrinkles, leading to premature aging of the skin. They promote triggering of the erythemal reaction or amplify this reaction in the case of certain individuals and may even be the cause of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons such as the conservation of the natural elasticity of the skin, more and more individuals wish to control the effect of UV-A rays on their skin. It is thus desirable also to screen out UV-A radiation.
There is at the present time an ever-increasing need for aromatic compounds that are effective at screening out UV-A radiation and preferably in the range from 340 to 400 nm (range known as long UV-A or UV-A-I). Besides their good photoprotective efficacy in this range, the desired UV-A screening agents should have good cosmetic properties, good solubility in the usual solvents and in particular in fatty substances such as oils and fats, good resistance to water and to perspiration (remanence) and also satisfactory photostability.
A limited number of organic compounds that are effective towards UV-A rays and especially long UV-A rays are currently available on the UV-screening agent market.
In this regard, one family of UV-A screening agents that is particularly effective in the UV-A range currently includes dibenzoylmethane derivatives, and especially 4-tert-butyl-4′-methoxydibenzoylmethane, which specifically have good intrinsic absorbing power. These dibenzoylmethane derivatives, which are now products that are well known per se as screening agents active in the UV-A range, are described especially in FR-A-2,326,405 and FR-A-2,440,933, and also in EP-A-0-114,607; 4-tert-butyl-4′-methoxydibenzoylmethane is moreover currently sold under the trademark “Parsol 1789” by Hoffmann LaRoche.
Unfortunately, it transpires that dibenzoylmethane derivatives are products that are relatively photosensitive to UV-A radiation, i.e., more specifically, they have an annoying tendency to be degraded more or less quickly by the action of this radiation. Thus, this substantial lack of photochemical stability of dibenzoylmethane derivatives with respect to ultraviolet radiation, to which they are by nature intended to be subjected, does not make it possible to ensure constant protection during prolonged exposure to the sun, and as a result the user needs to make repeated applications at regular and short intervals in order to obtain effective protection of the skin against UV rays.
Another difficulty, which is independent of the one mentioned above, encountered with dibenzoylmethane derivatives is that they are lipophilic screening agents that have the particular feature but also the drawback of being solid at room temperature. As a result, their use in an antisun or sunscreen cosmetic composition entails certain constraints as regards their formulation and application, in particular when it is a matter of finding solvents for dissolving them correctly, alone or in combination with other screening agents.
Thus, need continues to exist for novel families of aromatic compounds that are effective in terms of screening in the UV-A range and especially the long UV-A range, but which are photostable and also have good solubility in the usual solvents, good cosmetic properties and also good resistance to water and to perspiration (remanence).